"When I got the green light, I was (able) to go. The fight was over. It was real quick," he said. "(Stone) knocked out one guy, after he got stabbed like three or four times."

Hailermariam said the fight was three against one.

"He (Stone) tried to protect himself.

Sacramento police said a 24-year-old woman was also hurt during the fight.

Hailermariam said the woman was trying to protect Stone after he was stabbed.

"She got a big hit. She got one big punch."

After the fight, Hailermariam said he asked Stone if he needed a ride to the hospital, but another member of the group had already called 911.

Stone, an Airman First Class with the U.S. Air Force, was one of three Americans who helped thwart a terrorist attack on a train in France in August.

Officials at UC Davis Medical Center said he was admitted to the hospital early Thursday morning with three stab wounds to his torso and underwent successful surgery.

He remains listed in serious condition, but is expected to make a full recovery.

Sacramento police, meanwhile, are searching for two men involved in the stabbing.

Deputy Chief Ken Bernard said the men were described as wearing white T-shirts and blue jeans. They were last seen driving away from the scene in a 2009 to 2012 dark-colored Toyota Camry.

“The assault does not appear to be a random act. It is believed to be related to a nightclub incident,” Bernard said during a news conference Thursday. "This incident is a very unfortunate altercation between two groups of folks enjoying the nightlife in Midtown. It is not related to terrorism in any way."

Police also tweeted that "alcohol is believed to be a factor" but have not said what triggered the attack.

Surveillance video released by A&P Liquor shows a group of men going after a single man, who is believed to be Stone.

A man and a woman were initially questioned by police, but they were not detained.

Sacramento Mayor Kevin Johnson tweeted his support for Stone: "My thoughts and prayers go out to Spencer Stone and the Stone family. I ask that everyone respect the family's privacy at this time."

Stone and two friends, Anthony Sadler and Alek Skarlatos, who all grew up in Sacramento, were hailed as heroes for stopping a terrorist attack on board a Paris-bound train.

Skarlatos tweeted Thursday morning, "Everybody send prayers out to the Stone family today."

The trio were celebrated on Sept. 11 with a parade through downtown Sacramento.

However, Skarlatos had a tough week last week after learning his college in Roseburg, Oregon, Umpqua Community College, was the site where a gunman opened fire, killing nine people before turning the gun on himself.

Skarlatos spoke with KCRA's David Bienick last week about how he was coping with the tragedy.

Anyone with information about the stabbing or the fight is asked to call the Sacramento Police Department at 916-443-4357.

The Air Force said people who want to write to Stone can email him at airmanstone@us.af.mil.